岩溶地区土状堆积物物质来源判别的实用指标——粒度分布特征

PRACTICAL INDEX TO DISTINGUISH THE ORIGIN OF EARTHY DEPOSITS IN KARST AREA -CHARACTERISTICS OF GRAIN SIZE DISTRIBUTION

选择湘西吉首完整的灰岩风化壳 ,首次利用粒度参数并结合已有的矿物学、地球化学的研究成果 ,为湘西和贵州地区的碳酸盐岩上覆土状堆积物的残积成因提供了有力的佐证。粒度分析研究结果表明 ,湘西吉首灰岩风化壳基岩酸不溶物及其上覆半风化带粒度频率分布曲线形态的一致性和渐变性 ,指示了风化壳对基岩的继承和演化 ;砂 -粉砂 -粘粒含量、中值粒径和平均粒径在剖面上的演化趋势 ,反映了一个标准残积风化壳的发育规律 ;频率曲线众数峰含量随深度的变化 ,不但指示了化学风化趋势 ,而且反映了风化程度的变化梯度。

This paper selects intact limestone weathering profile in Jishou of Xiangxi to measure grain size parameters. To study residual weathering crusts, people often investigate it by incorporating field survey with mineralogy and geochemistry. This is the first time to do the study by means of combining grain size parameters with available mineralogy and geochemistry results. We clearly demonstrate that the earthy deposit overlying on the carbonate rocks in Xiangxi and Guizhou is formed by residuals. This study shows that grain size frequency curves of the acidic insoluble material from bedrock and overlying semi weathering section are consistent with each other and are of gradually changing characteristics,which indicate that the weathering crust inherits and comes from bedrock. The variation trends of sand, silt and clay content, median and mean grain size with the increasing of depth, reflect the developing rule of a standard residual weathering crust. The variation of frequency curve's mode peak content with the increasing of depth, shows not only the trend of chemical weathering but also variation gradient of weathering extent.